It should be pointed out that the cereals or other plants, for example, barley, even before undergoing the different operations of treatment and transformation in a malting unit are naturally contaminated with many micro-organisms. Thus, in the particular example of barley, this latter is the natural host of a diverse and considerable flora which is composed, principally, of bacteria and yeasts as well as filamentous fungi. Indeed, this flora contaminates and colonizes the barley grain both in the field as well as during storage. The nature and number of these micro-organisms depend, of course, on the conditions of cultivation and climate, as well as on the duration and conditions of storage.
The various analyses performed on these micro-organisms derived from the fields has enabled about a hundred species to be listed. However, the most frequently encountered moulds are Alternaria, Clasdosporium and Fusarium.
Moreover, it has been observed that in the case of a late harvest or when the harvesting is done in wet weather, the grain exhibits considerable contamination with Fusarium. As for the flora which contaminates and colonizes the grain during storage, thus prior to malting, it is composed of xerophilous filamentous fungi. There again, the study of these filamentous fungi has made it possible to demonstrate that the predominant species are Aspergillus and Penicillium.
Ultimately, the problem resides in the fact that the different operations which consist in transforming the cereals, in particular, into malt, are performed under conditions which promote the growth of the microflora already present on the grain. Actually, during the malting, conditions exist, particularly in respect to moisture, temperature, nutrients or also the residence time in the various vessels, which finally allow the bacteria and yeasts to multiply on a scale ranging from 10.sup.2 to 10.sup.4 without taking in account a considerable growth of moulds.
In this connection it is worthwhile recalling the different stages of the malting process. More precisely, after preparation of the grain, the latter undergoes a steeping operation for a period of about forty hours, in order to increase the moisture content by 35 to 45%. Then follows the germination during a period of about six days at a temperature of about 16.degree.. After that, kilning of the malt is performed which consists of drying the grain at different discrete steps of temperature, increasing from about 50.degree. to 80.degree. Celsius. Then follow deculming and the storage of the malt finally obtained.
This uncontrolled growth of the microflora constitutes a drawback as far as it affects the quality of the malt and, of course, of the final product, for example the beer which is obtained from it. Indeed, it is responsible for the production of inhibitors of germination. Moreover, it results in a production of undesirable enzymes such as lipases, oxidases, proteases, etc. Some of these micro-organisms present in an overabundant quantity are also responsible for undesirable flavors. The beer finally obtained may, thus, possess a musty or even earthy or oxidized flavor.
Generally in the brewing area the phenomenon of gushing is dreaded which, as its name indicates, consists in the beer gushing out of the bottle when it is opened, owing to an instability of the carbon dioxide. Indeed, specific micro-organisms are responsible for this. Consequently, it is advisable to avoid their presence or at the very least prevent their quantity from exceeding a given threshold. Now the only way to be sure of achieving this result consists in avoiding substantial growth of the micro flora and hence of the precursors of gushing produced in particular by Fusarium.
To this it may be added that the presence of certain micro-organisms such as the bacteria of the Pediococcus type has consequences on the filtration rate of the mash and leads to a rapid clogging of the filters.
However, the major drawback encountered as a result of the large growth of moulds consists of a large increase in the risk of formation of mycotoxins since toxicogenic moulds are naturally present on cereals and plants.
Indeed, inspite of the drawback previously mentioned, this growth of the microflora is scarcely controlled in the malt houses. The fault responsible for this is the absence of effective means to actually perform this control.
Thus, only a disinfection operation can be conducted at the time of steeping by the addition of hypochlorite or limewater. If the addition of such disinfectants has only a slight effect on the microflora, it presents no less a risk for certain operations of the malting process. In particular in the case where well-defined doses are exceeded, these disinfectants represent a risk for the germination of the grains and may lead to problems of off-taste in the beer for example.
The objective of the present invention is to remedy all of these drawbacks by preventing the growth, more particularly, of the undesirable microflora, through the inoculation of a specific micro-organism which has been selected in the light of the convincing results to which it has led.
It has been suggested to use in a malting process an inoculation of starter culture containing Geotrichum candidum to control the growth of the microflora.
The use of lactic acid bacteria which is widespread in the agrifoodstuff processes and even in malt-houses to produce acid malts, has been suggested for the reduction of the growth of fungal flora, in particular of Fusarium (WO 94/16053). However, the inoculation of lactic acid bacteria during malting only permits a partial inhibition of the growth of the fungal flora and does not make possible the inhibition of the mycotoxins during the malting process.
Geotrichum candidum which is naturally present on barley during germination and on the finished malt has been suggested, on the one hand, to inhibit the growth of toxicogenic flora during malting and the synthesis of mycotoxins and, on the other, to improve the biochemical and physico-chemical quality of the malt.
Geotrichum candidum is very common in the dairy environment. Most of the strains have been isolated from milk and cheese. It forms part of the flora naturally present in the manufacture of cheese from raw milk. In the dairy industry attempts have been made for a long time to prevent the growth of this yeast-like fungus which, poorly controlled, is capable of causing defects in the appearance of the cheese. In recent years we have witnessed on the part of the industrial cheese-makers a revival of interest in Geotrichum candidum owing to its role in the improvement of the organoleptic qualities of the cheeses and the inhibition of the growth of pathogenic bacteria and undesirable moulds in the ripening process.
The lipase activity of this micro-organism, in great demand in the cheese industry, was considered as a major drawback in the field of malting, in particular for the organoleptic adverse effects to which it can lead (Drost et al. ASBC Journal, 1990, 124-131; Kobayashi et al. Journal of Fermentation and Bioengineering, 1993, 371-375).